Conventional water treatment processes include aggregation, precipitation, filtration and disinfection, and the main treatment targets are limited to suspended materials and pathogenic microorganisms inactivated by chlorine disinfection. However, the water quality of raw water is increasingly deteriorating due to industrialization, population growth and the like, and existing water treatment processes expose their limits as various contaminants that have not been considerably questioned or detected have now surfaced as new harmful substances with the development of medicine, chemistry and analysis instruments.
Particularly, the circumstances regarding small-scale water supply facilities are more serious, and the facilities themselves have deteriorated as well as being very inferior. In addition, water sources are rivers, shallow underground water, wells, or the like, and therefore the water quantity and water quantity changes are extremely variable, and the water is exposed to the possibility of contamination due to nearby domestic sewage, livestock wastewater, agricultural chemicals or the like.
Accordingly, the introduction of a new water treatment process to solve the problems of small-scale water treatment facilities is urgently needed, and the introduction of advanced water treatment processes such as a biological activated carbon processes or advanced oxidation processes using ozone have been tried so far. However, these processes are not suited for small-scale facilities, and are usually introduced to purification plants of a relatively large scale.
Developed countries such as the US and Japan are currently introducing a membrane separation process as a water treatment process in order to solve such problems. A membrane separation process is usually removing contaminants according to membrane pores and molecular weight cut-offs in water quality, therefore, almost all pathogenic microorganisms as well as turbidity and algae may be removed when proper membranes are selected depending on the water quality of the target water treated. Cryptosporidium, giardia or the like that are not inactivated by chlorine disinfection, which have recently been an issue in the US, Japan and the like, may be effectively removed just by microfiltration, and may be almost completely removed when ultrafiltration is used, and almost all viruses are also removed by ultrafiltration. In addition, a membrane separation process may readily form a hybrid system with other physicochemical treatment processes and thereby may relatively readily improve water quality by adding proper treatment processes for contaminants to treat, and may obtain the target water quality.
Meanwhile, microfiltration/ultrafiltration membranes normally used in water treatment currently may remove almost all of the turbidity, bacteria, insoluble iron and manganese, algae and the like, however, colors and precursors of disinfection byproducts (e.g., trihalomethane) remain in water, and these are pointed out as being a problem of water treatment processes using a membrane. Nitrate or heavy metals such as iron, manganese and the like in purified raw water are considered as problems particularly in small-scale purification plants, and these microcontaminants are difficult to remove by a single membrane process. Accordingly, membrane fouling may be controlled by changing physicochemical properties of several membrane fouling materials and particulates by chemical coagulation in order to control specific materials and membrane fouling, however, large amounts of chemical sludge are generated. Particulates may be controlled by sand filtration or fiber filtration, however, sand layer blockage and short circuit phenomena in operation and backwashing processes, and entanglement of fibers are pointed out as operation problems. Adsorbents, such as powdered active carbon and metal oxide may be used as pretreatment, however, recovery and regeneration of used adsorbents, and the like, are a big obstacle.
In view of the above, the inventors of the present invention have developed a method of granulating inorganic adsorbents, controlled membrane fouling and demonstrated improved water treatment efficiency using the granular oxide adsorbent as a pretreatment before membrane filtration, and thereby completing the present invention.